In the development of semiconductor devices having highly integrated elements, each element is made finer, and the operating voltage is reduced. For example, in the field of MONOS (Metal Oxide Nitride Oxide Semiconductor) type nonvolatile semiconductor devices, as elements are made finer, a blocking film for separating a charge retention layer and a gate electrode is required to have a high dielectric constant. Similarly, in the field of FG (Floating Gate) type nonvolatile semiconductor devices, as elements are made finer, an insulating film between a floating electrode and a gate electrode is required to have a high dielectric constant. In the field of the development of advanced CMOS devices, investigations have been made on a technique of reducing gate-leakage current by using a high dielectric constant material to increase the physical thickness of a gate insulating film. Such a high dielectric constant film is also required to be heat-resistant to annealing at 1,000° C. in the process of manufacturing the above semiconductor devices. In addition, such a high dielectric constant film is also required to have high surface flatness in order to reduce fluctuations in the operating voltage of the semiconductor devices.
To increase the relative dielectric constant of dielectric films, methods using HfO2, ZrO2, or Al2O3, which has a relative dielectric constant higher than that of a conventional SiO2 or SiN film or a SiON film (a combination thereof), for dielectric films have been investigated. Recently, to reduce leakage current associated with a reduction in the dielectric film thickness, investigations have also been made on dielectric films having a laminated structure of HfO2, ZrO2 or Al2O3 or comprising HfO2 or ZrO2 doped with a metal element.
Methods for forming high dielectric constant films include CVD (Chemical Vapor Deposition) methods, atomic layer adsorption/deposition methods, and sputtering methods. CVD methods have incubation time in the deposition process and therefore present challenges in achieving film-thickness controllability, in-plane uniformity, and reproducibility. On the other hand, sputtering methods have the problem of plasma damage or the formation of an interface layer by oxidation of the treated substrate.
For example, Patent Document 1 discloses a technique of forming a dielectric film with a high dielectric constant by ALD or CVD method, in which the dielectric film is an amorphous film comprising an crystalline dielectric material and amorphous aluminum oxide and having the composition of AlxM(1-x)Oy, wherein M is a metal capable of forming a crystalline dielectric material, such as Hf or Zr, and 0.05<x<0.3. This technique is characterized in that amorphous zircon aluminate with a high relative dielectric constant of 25 to 28 can be obtained. Patent Document 1 also discloses that ZrO2 has a relative dielectric constant of 30.
For example, Patent Document 2 discloses a technique of forming a dielectric film with a high dielectric constant by sputtering, in which ZrO2 is formed by electron cyclotron resonance-assisted sputtering in such a range that the stoichiometric composition is achieved and in such an oxygen feed rate range that the rate of the reduction in the sputtering rate caused by oxidation of the target surface reaches the maximum.
Patent Document 3 discloses that a dielectric film comprising HfO2 doped with nitrogen and yttrium (Y) as a metal element is formed using HfO2 and Y2O2 ceramic targets as sputtering targets. Patent Document 3 discloses that when an element with a large atomic radius, such as Y, is added to monoclinic HfO2, the cohesive energy of the cubic crystal is reduced so that the cubic crystal is stabilized, which results in the conversion of the HfO2 crystal system from the monoclinic crystal to a tetragonal or cubic crystal, so that an HfYO dielectric film with a high relative dielectric constant of 70 is obtained. It is also disclosed that as oxygen in the monoclinic HfO2 is replaced with nitrogen, the nitrogen content increases, so that the crystal system changes from the monoclinic crystal to a tetragonal, rhombohedral or cubic crystal.
Patent Document 4 discloses a dielectric film comprising ZrxSi(1-x)O(2-y) (0.81≦x≦0.99, 0.04≦y≦0.25) which is formed by a process comprising forming an amorphous film in an atmosphere of a mixture of argon and oxygen by sputtering method using Zr and Si targets and then annealing the amorphous film under an oxygen-containing atmosphere at 750° C. or more to form a dielectric film having a tetragonal crystal.
Non-Patent Document 1 discloses a dielectric film composed of HfO2 formed by RF sputtering method and TiN placed on the surface of the HfO2. The document 3 discloses that when a laminate of HfO2 and TiN is crystallized, HfO2 having a cubic crystal phase is formed so that a dielectric film with a relative dielectric constant of 50 is obtained.